Most of the IT world breathed a sigh of relief today as last month's mysteriously delayed security updates for Windows finally arrived.

But without any fanfare, Microsoft tossed in a couple of additional surprises to celebrate this month's Patch Tuesday.

First up was a small notice in Windows Update offering early access to the next big feature update of Windows.

Windows Update is now offering advance notice of the imminent arrival of version 1703.

That's considerably more subtle than the pop-ups that appeared in advance of previous updates.

It appears in Windows Update, beneath the Update History link. On my test system running the latest Current Branch build, Windows 10 version 1607, it was only visible after I had successfully installed the latest cumulative update and then returned to Windows Update.

The "Yes, show me how" link leads to a fairly bland "Coming soon" web page offering a few details about the upcoming release of version 1703 and information on how to get an early look by signing up for the Windows Insider Program. (If you follow my Windows 10 tips collection, you already had detailed instructions on how to cut to the front of the line.)

Today's other Windows Update news is potentially far more significant, especially for harried IT pros trying to stay on top of the new Windows-as-a-service release cycle.

The first "delta updates" for Windows 10 version 1607 and Windows Server 2016 are now available in the Microsoft Update Catalog. If you search for KB4013429 (the official Knowledge Base ID for the March 2017 Cumulative Update to Windows 10 version 1607), this is what you'll see.

This month marks the first time that smaller delta updates are available for download.

The full Cumulative Update packages, listed in the bottom of the list, is a hefty one indeed. For the 64-bit editions, the download is well over 1 GB in size, and even the 32-bit version clocks in at over half a gigabyte.

By contrast, the corresponding delta update packages are about one-third smaller for 64-bit packages and nearly 40 percent smaller for 32-bit Windows 10 installations. These packages are applicable on any Windows 10 device that already has the previous Cumulative Update installed.

The bandwidth savings really add up when you realize that an IT pro can download one of the update packages, post it on a network share, and manually update machines.

The delta update packages address an inevitable by-product of the Windows-as-a-service model. Each month's Cumulative Update includes all security and reliability fixes from previous monthly updates.

That means each Cumulative Update gets progressively bigger. The first Cumulative Update for the 64-bit version 1607, released in August 2016, was a mere 113 MB. By November, it was 871.8 MB, and four months later it was over a gigabyte.

Fortunately, that's about as big as those cumulative updates get. The update size for the 64-bit Windows 10 version 1511, which is nearing the end of its supported life, is now at 1079.9 MB. That's up only about 100 MB in the past six months.

Alas, a delta update won't be available for the Creators Update. That functionality is currently available only for monthly Cumulative Updates. When version 1703 hits Windows Update in April, it will be roughly 3 GB in size.

These delta updates are a small step on the road to something much more efficient. Version 1703 will include architectural changes that will make the next big feature update, at the end of this year, significantly smaller. That feature, called the Unified Update Platform (UUP), will begin rolling out as part of the Creators Update, version 1703.

Microsoft says UUP will cut the size of feature updates by approximately 35 percent. And the changes don't stop there. It will also allow differential monthly updating that will shave the size of monthly quality updates, delivering Express Updates that are roughly 100 MB in size on systems that are otherwise up to date. Microsoft says those changes will appear first in Windows Insider preview builds later this year.

Do CIOs care about Windows 10?

Meanwhile, if you're an IT pro, it pays to keep an eye out for those leaner update packages.

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